It is estimated that over 20% of fatal cancers or about 2.1 million cases per year worldwide can be attributed to viral or bacterial infections, suggesting the tremendous potential of controlling microbe-related processes for cancer prevention. Although viral infections have been associated with cancer, the involvement of bacteria has also recently received attention, and there is increasing evidence to suggest that studies on the role of bacteria in cancer progressions are warranted. Important mechanisms by which bacterial agents may promote carcinogenesis include chronic infection, inflammation, immune evasion and immune suppression. Our overall hypothesis is that the bacterial colonization is associated with chronic inflammation which has the capacity to support oral squamous cell carcinomas (OSCC) progression. The oral cavity and OSCC represent a unique opportunity to study the bacterial association with cancer because: (1) the microbiota of the oral cavity is well documented;and (2) the ease of sample collection. In Aim 1, we hypothesize that the bacterial colonization is altered in OSCC and dysplasia as compared to adjacent normal mucosa. We will determine the difference between the bacterial colonization (cultivable and non-cultivable) in OSCC, epithelial dysplasia, vs. adjacent normal mucosa. Using 400 bp fragments of the 16S rDNA gene and high throughput 454 pyrosequencing we will determine the relative abundance and species richness of the bacterial population in these sample groups. Artificial Intelligence analysis will be used to discover a pattern of bacterial phylotypes that are represented in OSCC, epithelial dysplasia, and normal mucosa. In Aim 2, we hypothesize that the colonization of dysplastic lesions and OSCC by bacterial pathogens is associated with chronic inflammation. We will use immunohistochemistry to compare the composition and quantity of the inflammatory cell infiltrate and evaluate the cytokine profile in the same tissue samples of OSCC, dysplasia, and normal mucosa used in Aim 1. The differences in bacterial profile between OSCC tissue and normal mucosa and the similarities in bacterial profile for OSCC and dysplasia will be used to develop a bacterial profile of OSCC which in association with inflammatory factors will serve as an indicator of risk for OSCC. We expect that understanding the impact of oral bacteria on the development of OSCC will open novel approaches to direct the course of future interventions and prevention strategies by controlling the infectious agent, which are the approaches now used for managing Helicobacter pylori related gastric cancer. Public Health Relevance: Understanding the impact of oral bacteria on the development of OSCC will lead to patient oriented research where one may be able to assess OSCC risk by measuring bacterial profile in oral tissue of a person. The study will direct the course of future intervention and prevention strategies for this pathological condition.